1. Field of the Invention
The invention relates in general terms to the production of patterned optical coatings on substrates; in particular, the invention relates to the production of areally patterned, in particular segmented optical filter layers on substrates.
2. Description of Related Art
Areally segmented optical coatings on substrates are required, inter alia, for optical filters, such as for example optical rotary filters or color wheels for video projectors. A filter of this type sequentially filters light rays of different colors out of a light beam and projects them onto a screen by means of a digital micromirror device (DMD).
For the sequential filtering, a color wheel of this type is divided into various segments which filter out the different colors depending on the position of the rotating color wheel. To generate a flicker-free image at least of video quality, the light has to be broken down into different light rays of different color very quickly. This requires rapid rotation of the filter and, associated with this, inter alia accurate alignment and balancing of the filter disk, so that the latter is able to withstand the mechanical loads which occur during rotation. A further requirement for color wheels of this type is that the transition between the individual segments be as seamless as possible.
In a conventional process for producing a filter of this type, various filter disks which have in each case been uniformly coated and have defined filter properties, are cut into segments and the segments are then assembled again to produce a filter disk. Color wheels of this type and processes for producing them are known, for example, from DE 19708949 A1 and U.S. Pat. No. 5,868,482 A. However, the cutting and assembly operations are complex, and in particular assembly requires particular care, since firstly it is necessary for the transition to be as seamless as possible, and secondly accurate balancing of the assembled filter disk is required. Furthermore, the join between the individual segments also has to withstand the mechanical loads which occur during rotation.
Another possible way of producing a color wheel is to provide a substrate with segmented filter layers. For this purpose, it is known from WO 99/42861 A1, to provide the substrate with a color filter layer system by means of the lift-off technique. The filter layer is produced by sputtering or plasma-enhanced vapor deposition. By then dissolving the photoresist masking and lifting off the filter layer thereon, a segment of the filter layer is left in place on the substrate. This process is repeated for each filter segment. However, the process is restricted to use at low substrate temperatures below 150° C.